In applications such as the formation of pMOS metal gates, it is generally desirable to deposit a metal with a high work function and a low resistivity. A high work function allows for a lower threshold voltage offset and a lower off current. From this, a lower leakage current can be achieved and a threshold voltage swing can be improved. A low resistivity positively affects a cycle time and allows for higher speed processing.
Formation of Titanium Nitride (“TiN”) films has been achieved using different methods. However, the TiN films created have exhibited different work functions based on the method used. For example, TiN films created through Atomic Layer Deposition (“ALD”) have demonstrated work functions ranging between 4.70 and 4.75 eV. TiN films created through plasma treatment with hydrogen gas in an EmerALD® XP Process Module from ASM International have demonstrated a work function of approximately 4.96 eV. TiN films created through Plasma Enhanced Atomic Layer Deposition (“PEALD”) treatment with Tantalum Carbon Nitride (“TaCN”) in an EmerALD® XP Process Module have demonstrated a work function of approximately 5.00 eV.
While the TiN films created through the plasma or PEALD treatment have exhibited higher electronic work functions, plasma treatments have been discouraged for pMOS metal gate applications due to concerns over plasma damage. In addition, the plasma treatments result in films with a greater Effective Oxide Thickness (“EOT”), which is known in the art as a thickness of a silicon oxide film required in order to produce the same effect as a high-k material being used. A greater EOT is undesirable because it leads to a reduced capacitance.
Accordingly, a method that creates a metallic film with a high electronic work function, low resistivity, and lower effective oxide thickness is desired.